There are a great many devices adapted for thermal spraying using a plasma arc gun. For an example, see U.S. Pat. No. 6,897,402 to Crawmer.
Typically, these devices use a cathode and anode combination that defines a chamber through which gas is flowed. During operation, electricity is passed between the cathode and the anode, forming an arc that energizes the gas to form plasma. A continuous stream of gas is supplied to the gun, formed into plasma, and then ejected from the plasma gun.
When used for coating, these devices are adapted with a port configured to deposit powder into the stream of plasma prior to ejection from the gun. As powder material is deposited, the powder grains partially melt. The stream of plasma and melting particles is directed from the gun through an atmosphere where it cools slightly, and onto a surface where it sticks and hardens to form a coating.
At typical energies, full melting and vaporization of the coating material does not occur prior to ejection. Unfortunately, some applications, such as powder production (as opposed to coating), require full vaporization to achieve desired purities or small grain sizes. A naive route to achieve full vaporization dictates simply running a plasma-arc gun, such as a Crawmer-like device, at higher power. However, because the vaporization points of the materials used in powder production applications are often very high, the power necessary to achieve full vaporization of commercially available powders would destroy the device.
What is needed in the art is a system for and method of achieving full vaporization of powders, while minimizing the wear on the plasma-arc gun.